1. Field of Invention
The invention relates generally to treating ischemic and anoxic brain injuries. More particularly, the invention provides an apparatus and method for cooling of the brain and maintaining it at a temperature below normal body temperature during trauma or other periods of decreased or compromised blood flow due to, for example, stroke. With the invention, the brain and associated neurologic tissues survive the anoxic or ischemic trauma intact. The victim recovers with increased chances of survival and less chance of pennanent brain damage.
2. Description of Related Art
When an ischemic or anoxic injury occurs, the brain is deprived of freshly oxygenated blood. For example, this situation typically occurs during cardiac arrest, respiratory arrest, stroke and other cerebrovascular trauma, suffocation, drowning, strangulation, electrocution, toxic poisoning (carbon monoxide, cyanide, etc.), metabolic insults or other similar trauma. Without a steady supply of freshly oxygenated blood, the brain ceases to function and after resuscitation, most patients will suffer some damage to the brain and associated neurologic tissues.
For example, among cardiac arrest victims overall less than 10% survive neurologically intact and without significant brain damage. The other approximately 90% either die or sustain some neurologic injury from ischemia (i.e., lack of blood flow to the brain), or anoxia (i.e., lack of oxygen to the brain). Such frequency of neurologic injury occurs because after a cardiac arrest, basic cardiopulmonary resuscitation and advanced life support techniques, such as CPR, closed heart cardiac chest massage, and electroshock treatments, typically require fifteen to twenty minutes to regain circulation from a failed heart. Reversible neurologic damage begins as early as four minutes and irreversible neurologic damage begins as early as six minutes after circulation stops. To combat this potential neurologic injury, initial resuscitation efforts need to be directed toward reviving the brain in addition to resuscitating the heart.
As indicated above, anoxic and ischemic brain injuries from cardiac arrest, stroke or the like result in damage to the brain and associated neurologic tissues after about four minutes. In contrast, the heart can survive intact up to four hours after cardiac arrest, stroke or the like. The short viability of brain tissue upon deprivation of oxygenated blood is a result of the requirement of high amounts of nutrients for tissue maintenance. Brain tissue uses almost all of the nutrients supplied by the circulating blood for maintenance and stores only a small amount of nutrients. Absent blood flow to the brain, the small amount of stored nutrients is rapidly exhausted. Once exhausted, brain oxygen content is rapidly depleted. This oxygen depletion is traumatic and causes a series of reactions in the oxygen starved brain tissue cells. These reactions are believed to produce free radical ions, primarily consisting of the superoxide radical O.sub.2 --.sup.-. These free radicals complex with proteins in the brain and associated neurologic tissues, altering respiration, energy transfer and other vital cellular functions, and irreversibly damage these tissues.
Efforts should be directed toward resuscitating the brain to attempt to extend the period of time the brain can function without oxygen while the patient remains neurologically intact. The medical literature is replete with examples of humans surviving extended periods of time (greater than 5 minutes) without oxygen being delivered to the brain.
Hypothermic therapy is one method of keeping the brain alive absent oxygen. It involves cooling the brain to a temperature where its metabolic activity is decreased. When the brain's metabolic activity is decreased, it uses much less oxygen and stored nutrients are exhausted slowly, while production of irreversibly damaging O.sub.2 --.sup.- free radicals is slowed and almost completely ceased. Thus, upon resuscitating the body from trauma, the patient emerges neurologically intact. For example, children revived after hours of submersion in very cold water have fully recovered with little if any neurologic damage.
Cooling for hypothermic therapy is presently achieved by cold room technology involving a heat exchanger in a heart-lung bypass. The surgery involved with the cold room technology takes place in a room the size of a meat locker or large commercial freezer. Cooling is also achieved by traditional devices such as natural or synthetic ice packs. Both of these devices and methods have several drawbacks.
A major drawback with the cold room technology is that it is invasive and quite expensive. It involves a team of highly trained, skilled medical personnel to operate and supervise a standard heart-lung bypass machine. This technology is not portable as it is restricted to a surgical operating room setting. Also, cooling is progressive, not instantaneous. Natural or synthetic ice packs, although portable and non-invasive, are disadvantageous because they are messy and do not rapidly achieve the low temperatures required to hypothermically shock the brain. Additionally, ice packs are ineffective in extremely hot environments such as deserts because they melt rapidly.
Previous inventions, such as those described in U.S. Patents Nos. 5,149,321 to Klatz et al. ('321), U.S. Pat. No. 5,234,405 to Klatz et al. ('405) and U.S. Pat. No. 5,261,399 to Klatz et al. ('399), address the need to direct resuscitation efforts toward the brain, such that the victim can survive ischemic or anoxic trauma neurologically intact. Specifically, the '321 and '405 patents discuss devices and methods for resuscitating the brain such that its metabolism is slowed in order that the victim survive these metabolic insults neurologically intact. The '399 patent discloses a device and method for externally cooling the brain and associated tissues.
Along with brain cooling, it can be advantageous to cool internal organs in the body such that their metabolism is slowed in order that they survive these metabolic insults fully intact. Typical current methods for cooling organs include ice packs or large scale machinery, such as that disclosed in U.S.S.R. Patent No. 1138152A ('152). However, these methods and devices both have drawbacks. Ice packs are typically small in area, and when applied to a person, do not provide the rapid cooling necessary to slow the metabolism of internal organs. The device disclosed in the U.S.S.R. '152 patent exhibits the drawback of providing cryogenic cooling that is too extreme for organ resuscitation during metabolic insults. This device is not suited for field use, as it is a large structure restricted to clinical facilities capable of handling dangerous fluids such as liquid nitrogen. Moreover, it must be used by a skilled surgical team and maintained by skilled technicians.